The present disclosure relates to fracturing of polygon data, one application being microlithography. In particular, it relates to preserving data regarding edges and/or vertices of the original polygons as the polygons are triangulated and even if the results of triangulation are further fractured.
Microlithography is the process of writing a circuit design (sometimes called the geometry) onto a workpiece having a radiation sensitive layer. The workpiece is typically either a wafer upon which the design is written directly, or a photomask for use in exposing equipment, such as a stepper or scanner. The lithographic writing equipment writes the geometry onto the workpiece, using a laser or charged beam to expose a resist layer. This exposure changes the molecular composition of the resist. During the developing process for a positive resist, any resist that has been exposed will be removed. In some applications, a negative resist is used where the resist that was not exposed will be removed in development.
Photomasks are high precision plates containing microscopic images of electronic circuits. Photomasks typically are made from very flat pieces of quartz or glass with a layer of chrome on one side. Etched in the chrome is a portion of an electronic circuit design. This circuit design on the mask is also sometimes called the geometry.
Photomasks are used in wafer fabrication, mostly to make ICs (integrated circuits). ICs are used in many products like computers, calculators, cars, cameras, and stereos. Photomasks are also used to make flat panel displays, thin film heads, PC boards, etc.
During development, a customer designs a circuit using tools that digitally store the information. The customer then sends the digitized data containing the design for each layer to the mask maker or direct writing vendor. The data can be sent on a disk, magnetic tape, via Internet or dedicated lines.
The mask maker takes the customer's data and formats it for the actual tools or systems in which the masks will be made. This includes fracturing the data, sizing the data if needed, rotating the data if needed, adding fiducials and internal reference marks, and making a jobdeck, which includes instructions for the placement of all the different patterns on the mask.
Fracturing the data means translating the customer data into a language the write tool can understand. The writing system typically uses rectangles and trapezoids—so the customer data is divided up (fractured) into these shapes. The jobdeck with the fractured data is put on a data media and sent to the write area or pulled directly to the machines using network software.
During printing, additional pattern processing takes place. The geometries are spatially reorganized to match the writing sequence of the tool. For some systems, this means rendering the geometries into pixels to be imaged by the exposure system. For other systems, this means translating the geometries into a format appropriate for vector shaped beams (VSBs) or laser scanning.
In more detail, the typical fracturing process in lithography divides arbitrary polygons into rectangles and/or trapezoids as illustrated in FIG. 1 with horizontal trapezoidalization. Starting from each vertex, cut lines are generated in horizontal extent. Some algorithms have optimizations and rules criteria to suppress the generation of very narrow geometries (which may be harmful to the critical dimension, CD, on some writing systems), and also combine horizontal and vertical cut lines, but the basic principle remains the same. See, e.g., Nakao and Morizumi, “A Figure-Fracturing Algorithm for Generating High-Quality Electron-Beam Exposure Data”, Mitsubishi Electric Advance, Semiconductors Edition, Vol. 75 at 38-39 (June 1996).
In traditional fracturing of outlined polygons, the information as to which edges represent the true outline of the geometry and which edges are a result of the fracturing operation, is lost. As true outlines have an impact on CD on the mask and false (inner) outlines do not, true outlines must be rendered with highest precision possible, but that is not required with the false ones. If this distinction is not available, they must all be treated as potentially vital for CD and hence processed with high-precision, compute-intensive methods. This information would be valuable for, among other things, accelerating succeeding rendering and improving image processing on the image.
Classification of the edges of fractured geometry is not binary. Some edges could be both internal to the original polygon or belong to its true outline as in example 1B, edge (1-2) which is largely internal, but includes a true outline segment near (1). While one could imagine further subdivision of the geometries until all edges becomes unambiguous, such an algorithm could be become too immensely complex to support any polygon shapes and contain an arbitrary number of vertices.
Furthermore, the present algorithms have the side effect of generating new vertices. If new vertices are inserted on angled lines, one risks introducing grid snapping effects when they do not coincide with the design grid. Grid snapping can harm the fidelity of the mask and result in defects and circuitry malfunctions or in image interference effects, when the limits of numerical precision cause a vertex to move onto an actual or virtual grid. Image interference effects are particularly harmful to display applications.
An opportunity arises to improve fracturing approaches used in microlithography and increase processing speed. A further opportunity arises to retain useful boundary and/or original vertex information during fracturing. Better processing with reduced resources and equal or better critical dimension consequences may result.